A press of pressure cell type generally comprises a force-absorbing press body defining a press chamber. In the upper part of the press chamber, a press plate and a diaphragm of rubber or another resilient material are arranged, which together form a pressure cell. The pressure cell communicates with a source of pressure and expands when a pressure medium is supplied. In the lower part of the press chamber, a structural support or a tray is usually arranged, which comprises a bottom plate having a tray frame. The tray supports a forming tool, a workpiece or blank to be machined, and, generally, a mat of rubber or another resilient material covering the forming tool and the blank.
Presses of pressure cell type are used, among other things, when forming sheet-shaped blanks or workpieces, for example sheets of steel or aluminium, to short-series products within the aerospace and automotive industries. The sheet is placed in the press in such manner that one of its sides faces a forming tool. The resilient diaphragm is arranged on the other side of the sheet. A closed space between the diaphragm and the press plate located above the diaphragm constitutes the pressure cell and this space is filled during the forming process with a pressure medium. By pumping additional pressure medium into the pressure cell, the pressure is increased in the pressure cell and the resilient diaphragm is pressed during stretching against the sheet which, in its turn, is formed round or in the forming tool. When the sheet completely fits to the forming tool, the pressure in the pressure cell is released and the diaphragm is removed, following which the formed component can be taken out of the press. It is often desirable to obtain an efficient handling of the production flow and, thus, short cycle times.